SF6 gas / SF6 gas quality

Frequently Asked Questions

What is SF6?

SF6 is a synthetically produced gas. The SF6 molecule consists of one sulphur atom surrounded by six fluoride atoms.

Is SF6 harmful to health?

Pure SF6 is harmless to health. Due to its weight (5 times heavier than air) it concentrates in lower areas, displaces the air and thus the oxygen required for breathing. In these areas there is a risk of suffocation due to lack of oxygen.

What is SF6 gas used for?

The main field of application is electrical power engineering where it is used in gas-insulated switchgear and equipment as insulating and arc quenching gas. Other areas of application include particle accelerators, electron microscopes, X-ray systems, radar systems and medical technology.

Why is SF6 used in electric power equipment?

SF6 has very good insulating and arc quenching properties. This is why SF6 is used in gas-insulated switchgear and different electric power equipment such as circuit breakers and converters etc. Fields of application: medium and high voltage.

Why must SF6 be used in closed systems?

With a GWP value (Global Warming Potential) or CO2e (CO2 equivalent) of 22,800, SF6 is the most climate-damaging gas of all known greenhouse gases. 1 kg of SF6 in the atmosphere contributes to the greenhouse effect to the same extent as 22,800 kg carbon dioxide (CO2). The residence time in the atmosphere is 3,200 years. For this reason SF6 emissions, must be avoided wherever possible.

Why is SF6 used in gas-insulated switchgear (GIS)?

The use of SF6 gas enables to build compact switchgear and to achieve higher system voltages. In addition, increased equipment safety and reliability is offered in GIS.

How is used SF6 gas treated?

SF6 gas can normally be directly reused after filtering and drying with a gas handling unit. The limit values of the gas quality must correspond to the IEC 60480 directives. Only in exceptional cases is the preparation of SF6 gas not possible and the gas must be disposed of by thermal combustion. 

Are there emissions during measuring?

By using gas-tight and self-closing couplings and by returning the SF6 gas used for the measurement after the measurement (intermediate storage in an internal or external vessel), SF6 emissions can be avoided or reduced to a minimum.

What do I need to pay attention to during gas measurement?

In order to ensure a proper measurement result, attention should be paid to the following:

  • Only use pressure reducers with metal membranes,
  • Do not use any rubber hoses,
  • Only use self-closing couplings.

What is meant by dew/frost point?

The dew point/frost point is the temperature to which the gas must be cooled before water vapour either condenses or re-sublimates, depending on the temperature (formation of a layer of ice).

How can the dew point be determined?

Using electronic sensors (capacitive) of physically using a dew point meter.

In which units is the moisture indicated and are these pressure-dependent?

In dew/frost point (pressure-dependent) [°C/°F] or in ppmv or ppmw (pressure-independent).

How is the air content/CF4 determined?

Indirectly through determination of the SF6 volume (measured in percent).

Which is the most common measurement method for determining the air content/CF4?

Measurement of the velocity of sound in the gas.

When do decomposition products occur in SF6?

Decomposition products occur as a result of discharges/flashovers in the gas compartment.

What are the common measurement methods, in practice, for the identification of decomposition products?

The common methods are the use of electrochemical sensors or test tubes.

How is the concentration of decomposition products determined in practice?

The SO2 concentration is generally used as an indicator for the overall concentration of decomposition products (coefficient approx. 1:4), measured in ppmv.

How can decomposition products be removed from the gas?

Gaseous decomposition products can be filtered out using dry filters - in the form of dust - by means of particle filters. This occurs automatically during the recovery and filling process with a DILO service cart or interconnected filter units.